Bonds and rebar

Impact Constraint

An Impact Constraint node controls the glue bonds between neighbouring pieces. You can use several, each on a different group of pieces, so a mortar joint can differ from a brick.

Setting	Default	What it does
Constraint Type	Glue	How bonds behave under load: snap, bend permanently, or spring back.
Breaking Force	45	The tensile or shear threshold that breaks a glue bond.
Shear Strength Ratio	0.6	Shear strength as a fraction of tensile. Lower snaps more easily under sideways load. Concrete is about 0.6, steel 1.4, glass 0.3.
Stiffness	1,000,000	How stiff the bonds are.
Yield Strain	0.08	Strain beyond which bonds deform permanently.
Creep Rate	0.4	Rate of permanent deformation per second.
Sound Speed (m/s)	0	0 is an instant shockwave. Above 0, stress waves travel through the bond graph at that speed.
Wave Impact Speed	5	Approach speed that triggers a stress wave.
Fatigue Rate (1/s)	0	Damage from repeated sub-critical loads. 0 is no fatigue.
Fatigue Limit	0.5	Endurance limit as a fraction of the breaking threshold. Loads below it do no damage.
Fatigue Exponent (n)	4	How steeply damage scales with cyclic stress.
Bonds	Inside	Which bonds of the group these settings apply to.

Plastic deformation

With Plastic Deformation on (the Impact Solver’s default), glue bonds can yield. Stretched past the Yield Strain, they lengthen permanently at the Creep Rate. This gives bent metal and crumpled panels. Off, bonds stay elastic until they snap.

Stress waves

With a Sound Speed above 0, a blast or heavy impact sends a stress wave through the glued chunks. Bonds crack only once the wave reaches them, so a structure fails progressively instead of all at once. Concrete is about 3,400 m/s and steel about 5,100.

Impact Rebar

Impact Rebar adds steel reinforcement along a curve. The shards it passes through stay tethered after the brittle glue snaps. The bar is soft: it flexes, yields, and stretches permanently. It never breaks.

Setting	Default	What it does
Curve / Mesh	none	A 3D curve or edge-mesh object running through the shards.
Rebar Stiffness	200,000	Tether stiffness. Softer than the glue, so a bar flexes.
Yield Strain	0.1	Stretch, as a fraction of the bar length between two shards, beyond which the bar yields and elongates permanently.
Max Stretch	0.5	Most permanent elongation. Past it the bar is stiff again.
Creep Rate	0.3	How fast a yielding bar takes up its overstretch.
Rebar Links	2	Tether anchor pairs at each joint where the bar passes from one shard to the next. More resists bending.

You can also create rebar in the fracture tool with Curve or Auto Core Rebar.

The Reinforced Pillar template shows rebar: a concrete pillar with four steel bars, pinned top and bottom, smashed by a wrecking ball. The concrete breaks and the bars hold it.

Anchors

Pieces can be pinned so they never move, for example a wall’s footing. Use Pin in Place on an Impact Activation node. A pinned piece stays until a Trigger releases it.